I sometimes run across comments suggesting that replica firearms are "better" than the originals because modern steel is "better" than the steel used in the 1850s.
I also see videos where somebody loads tiny mounts of smokeless powder in their replica weapon and turn it into shrapnel.
I want to share my take on what is going on.
Some modern steels are designed to be brittle
Some modern steels are designed to be very easy to machine. That is, they consume relatively low amounts of power, the tool-edge stays sharp for a long time, the cuts can be made very quickly and the surface quality is so smooth that secondary polishing is unnecessary. Consequently, using these kinds of steels are very economical for the manufacturer as long as the pats are fit-for-use.
That is done by adding phosphorous and sulfur* back into the purified steel. Phosphorous and sulfur are USUALLY considered impurities because they make the steel brittle. Sometimes lead is added to the steel to act as a lubricant, almost like a mist of oil dispersed within the matrix of the steel.
When the edge of the tool is pealing off a layer of steel, the layer can either break-up into flakes shaped like grains of rice or grated Parmesan cheese, or the layer (called chips) can remain long and create friction against the surface of the tool and clog-up the tool.
Replica firearms use the European versions of the free-machining steels
You might take some section measurements, look up the mechanical properties and think everything is jolly. In fact, you might calculate that the chamber of an 1858 New Army replica SHOULD be able to sustain 16,000 lbs of pressure based on an internal-diameter of 0.445" and web thickness between the cylinders of 0.066" and a yield strength of 50,000psi (for cold-drawn bar).
The problem is that free-machining steels have HORRIBLE impact toughness. Tiny flaws (cracks, tool chatter marks, corrosion pits, threaded surfaces) can grow under load at the speed of sound. One measure of impact toughness is the Charpy-V test. That is where a sample with a flaw (a "V" shaped notch) is fractured and the energy required to break the sample is recorded.
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Both of them have Charpy-V impact strengths of more than 40 ft-lbs at 50 degrees F.
1215 which is a resulfurized and rephosphorized, free-machining grade of steel has a Charpy-V impact strength of about 3 ft-lbs at 50 degrees F. That is less than 10% of the energy required to propagate a crack through a sample of non free-machining steel.
So any minor notch-like feature (like the female threads where the nipple is installed) can make the chamber fracture almost as if it were made of glass...even if the back-of-envelop calcs say it SHOULD have been safe.
She didn't make it
The doe that didn't flee when I was working in the Upper Orchard at the property I am managing was not alive today.
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| Something has started eating her. |
*Adding sulfur also requires additional manganese to avoid hot-shortness, but the manganese, by itself, does not improve machinability.
Metallurgy today is almost light years ahead of what it was when Colt designed and built his Peacekeeper.... But the skills back then were still up to the task. The demands placed on firearms today aren't that much higher than then. So the metal doesn't generally need to be that much better. The attention is more on efficiency and cost savings, not strength. For the most part. A few calibers are of such higher pressure that the metals do need to be reconsidered. But Mr. browning designed his 50BMG a century ago...and metals then were up to task.
ReplyDeleteCutting tool technology has increased by a huge amount. Carbide and cermet and nitrides mean that pre-hardened materials (sometimes with very little alloying elements, just cold-drawn) can be used.
DeleteThere are now micro-alloyed materials that have tiny bits of boron in combination with nitrogen and pixie-dust...very economical.
Near-net shape technologies like investment casting has improved as has the ability to control temperatures.
Excellent points!
ReplyDeleteTo the comment about the 50BMG being designed a hundred years ago - (almoat) any metal will do if you use enough of it. My personal headache are the steel grades for low temperatures. Some of the stuff we make will go to Canada or Norway or the North Sea platforms and they are typically asking for the properties at -20 Celsius or at -40 Celsius (NL2 or NL4 steels). Brittleness is really a thing at those temperatures.
ReplyDeleteThanks for commenting!
DeleteIn the automotive world, a particularly challenging structure involved suspension parts that were MIG welded together. The steel types need to be high-strength, were subjected to impacts, in high-corrosion environments so were subject to hydrogen embrittlement and were welded which usually resulted in small cold-lap formations in highly stressed areas. The cold-lap looks exactly like a crack to the structure and cold-lap is almost inevitable at the start of a weld.
One supplier had a novel (to me) solution to the cold-lap issue. Rather than starting the weld where the two pieces meet, they started the weld on the thicker piece approximately 25mm from where the two parts butted-up. They put the "cold lap" on the thicker piece, well away from the joint. Then they ran a bead to the actual joint approaching it at 90 degrees, then turned and made the actual welded joint.
That had the effect of stabilizing the weld arc and preheating the thicker piece.
Seems I am always learning new interesting things here. Thanks Joe.
ReplyDeleteI know enough about blacksmithing to make a well tempered Mattox (and do minor repairs often on cheap steel tools) and not to put smokeless powder into a cap and ball revolver.
But I'd need a lot of research to really understand what you're discussing here. Interesting stuff.
Another issue today is that between recycled steel content, poor quality control/ testing, and outright fraud, almost no steel products are up to spec - alloy content may or may not be close, depending on the source.
ReplyDeleteI have investigated a couple of accidents where the material was way under the strength it should have been, and in particular they were MUCH more susceptible to stress fractures than they were supposed to be.
One was a beam 3 inches thick and 16 inches tall that failed catastrophically with no warning (or none obvious).
Companies that need specific steel types now test every piece coming in the door. XRF guns have become popular for this because they are quick and non destructive.
Jonathan
My take is thus: When you underload a cartridge, there is space in the case. Modern powders require pressure to burn as advertised. When the primer ignites, the initial pulse starts, the bullet speeds out and the pressure drops, the bullet stops in the bore becoming an obstruction. The pressure curve ramps up again, and the modern steel fails. This double bump pressure / bore obstruction makes perfect sense for a kablooie when coupled with the steel analysis you give. There is a point where being too frugal with powder breaks yer toys.
ReplyDeleteWhen I was learning to load and reload both black and smokeless powder 60 +_ years ago I was told to always fill the chamber/case and if the powder didn't do it to top it off with a filler such as Cream of Wheat. I worked for me but is that the right way to do it? ---ken
DeleteI believe it is. I've read the same, too. I'm cheap, but I didn't "undercharge" the cases.
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